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#1




Paradox unexplained
For the black hole information paradox I would expect
two seemingly conflicting results (as is necessary for a paradox by definition,) e.g. like: 1) We know that information is lost because [...] 2) But also that it is not lost because [...] Unfortunately I cannot find it clearly explained in that way. To be honest, I cannot even find the first statement clearly explained. What I mean is: by using KruskalSzekeres coordinates we can follow any molecule, or larger object, that enters the black hole, and there is no clear indication that it ever loses information at all! There might be tidal forces tearing it apart, but that need not in general destroy information and also that need not happen at the event horizon (in fact the Schwarzschild radius has no special local properties at all, as the KS coordinates prove). Finally, singularities may be present somewhere inside, but we don't know the physics there, so we cannot claim anything about what happens to information at those sites. Actually, for statement 2) I also never found a really satisfying explanation, but let's leave that out, since without *two conflicting statements* there is no paradox anyway. So why do people feel there is a paradox?!  Jos 
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#2




Paradox unexplained
On Friday, April 1, 2016 at 10:49:07 AM UTC4, Jos Bergervoet wrote:
So why do people feel there is a paradox?! You are correct in implying that this paradox cannot be satisfactorily answered using theoretical models  far too much uncertainty in any "conclusion". The first assumption: that information is lost, for many people, comes from variations on the following thought experiment. Throw an encyclopedia into a black hole. What is the probability that one could recover all the information exactly. Answer: either 0 or effectively 0. 
#3




Paradox unexplained
Op vrijdag 1 april 2016 16:49:07 UTC+2 schreef Jos Bergervoet:
For the black hole information paradox I would expect two seemingly conflicting results (as is necessary for a paradox by definition,) e.g. like: 1) We know that information is lost because [...] 2) But also that it is not lost because [...] Unfortunately I cannot find it clearly explained in that way. To be honest, I cannot even find the first statement clearly explained. Actually, for statement 2) I also never found a really satisfying explanation, but let's leave that out, since without *two conflicting statements* there is no paradox anyway. So why do people feel there is a paradox?! I understand your frustration. In a sense when there is an information issue for a BH than there should also be an information issue for the Sun. when you drive in a car our brain (via our eyes) continuously receives and creates new information and old information is erased and lost. From a physical point, in order to understand the universe, this information transfer process in our brain is completely unimportant. When a comet collides with the Sun, before that event, we are capable, based on a limited set of observations, to calculate the past and future of that comet outside that range. After the collision we know that the mass of the Sun has increased slightly and that the trajectory of the Sun was affected. But if we want to calculate the past of the Sun based on a limited set of observations (after this collision event) we can not do that accurately. The same problem exist for a BH. This has nothing to do that we humans cannot observe a BH. After a collision of a star with a BH the two melt together into one larger object and the physical details of each before the event are physical lost. That is the physical reality. In all these three cases I "see" no paradox. Nicolaas Vroom http://users.telenet.be/nicvroom/wik...on_paradox.htm 
#4




Paradox unexplained
On 4/1/16 4:47 PM, Jos Bergervoet wrote:
For the black hole information paradox I would expect two seemingly conflicting results (as is necessary for a paradox by definition,) e.g. like: 1) We know that information is lost because [...] We believe that matter in a pure quantum state can collapse to form a black hole. Such a black hole will then evaporate by Hawking radiation, which is thermal. When the black hole has completely evaporated, the net result will be the conversion of a pure state to a mixed state. This is what is meant by "information loss"  quantum mechanically, a pure state contains the maximum information about a system, while a thermal state contains the minimum amount of information. 2) But also that it is not lost because [...] Quantum mechanics is unitary. This means that the "finegrained" information in a quantum state is never lost; pure states evolve to pure states. (Think of this as a quantum version of time reversal invariance  if you are given a final state, you can in principle evolve it back to the initial state.) There are some obvious places to look for loopholes. I suspect that at least the obvious ones have all been analyzed to death, and all have unpleasant consequences. For instance, Hawking radiation might not really be thermal; but to get back enough correlations seems to require some very nonlocal interactions. [...] What I mean is: by using KruskalSzekeres coordinates we can follow any molecule, or larger object, that enters the black hole, and there is no clear indication that it ever loses information at all! There might be tidal forces tearing it apart, but that need not in general destroy information and also that need not happen at the event horizon (in fact the Schwarzschild radius has no special local properties at all, as the KS coordinates prove). Finally, singularities may be present somewhere inside, but we don't know the physics there, so we cannot claim anything about what happens to information at those sites. That's absolutely correct classically. The problem only appears quantum mechanically, when you allow black holes to evaporate thermally via Hawking radiation. Steve Carlip 
#5




Paradox unexplained
Op zondag 3 april 2016 23:33:21 UTC+2 schreef Steven Carlip:
We believe that matter in a pure quantum state can collapse to form a black hole. This is in a certain sense equivalent that a star collapses and becomes a neutron star Such a black hole will then evaporate by Hawking radiation, which is thermal. This is in a certain sense equivalent that a star explodes and becomes a super novae. The issue is if in either of these cases you can speak about information loss? To answer the questions you must have a clear definition of what information means and what a pure and mixed quantum states are. To start with the second, my interpretation of a pure quantum state is that an object as such is completely everywhere physical and chemical identical. They have no structure. The four important parmeters a Radius, Volume, Mass and density. In a pure quantum state object the density is everywhere the same. My interpretation of a mixed state is that it has a structure. For example in the Sun and in planets when you "travel" towards the center the density changes. When the density and chemical composition inside a BH is everywhere the same than the information content is zero compared to the encyclopedia britanica. The text of a book contains knowledge and information. Along that line when you burn a book it is information loss. IMO it is much more important to understand the intial conditions and the whole life cycle process of a Black Hole until his dead. I doubt if the concept of information is in anyway important in order to understand this physical process. When the black hole has completely evaporated, The issue is here how do we know that BH physical can evaporate and change into a gaseous (visible?) state. The problem only appears quantum mechanically, when you allow black holes to evaporate thermally via Hawking radiation. The problem is much more a physical, chemical problem. At the same time it is also an information problem in the sense that we cannot directly observe a BH. That means it is extremely difficult to observe that the life cycle time of a BH is finite. It is a murder without a body. For a star this is much simpler. Nicolaas Vroom 
#6




Paradox unexplained
In article , Nicolaas Vroom
writes: We believe that matter in a pure quantum state can collapse to form a black hole. This is in a certain sense equivalent that a star collapses and becomes a neutron star Such a black hole will then evaporate by Hawking radiation, which is thermal. This is in a certain sense equivalent that a star explodes and becomes a super novae. The issue is if in either of these cases you can speak about information loss? Especially with respect to information loss, the two cases are not equivalent in any meaningful sense. The whole informationloss problem stems from the fact that, at least classically, a black hole has no hair, meaning it is COMPLETELY characterized by charge, mass, and angular momentum. This is not the case for a neutron star. 
#7




Paradox unexplained
On 4/7/16 4:13 AM, Nicolaas Vroom wrote:
Op zondag 3 april 2016 23:33:21 UTC+2 schreef Steven Carlip: We believe that matter in a pure quantum state can collapse to form a black hole. This is in a certain sense equivalent that a star collapses and becomes a neutron star Not really. A collapsing star is very unlikely to be in a pure quantum state. Such a black hole will then evaporate by Hawking radiation, which is thermal. This is in a certain sense equivalent that a star explodes and becomes a super novae. No. Here things are very different, because a black hole has an event horizon. Think of the first photon coming out of a supernova. That photon will be correlated with the remaining bits of the star, which, in turn, affect the next photon coming out. This allows the second photon to be correlated with the first. Similarly, the second photon is correlated with the remaining bits of the star, so the third photon can be correlated with the first two. If the supernova explosion destroys the star completely, the photons that come out can still be highly correlated. A black hole is different. The first photon of Hawking radiation will be correlated with something, but the thing it's correlated with is behind the horizon. That means that it *can't* transfer the correlation to the next photon, at least not by any local physical process. So unlike the case of the supernova, there's no easy way for the Hawking radiation photons to be correlated with each other. That means that the correlations in the initial state that formed the black hole get lost. The issue is if in either of these cases you can speak about information loss? In the first case, there's "coarse grained" information loss  it's *hard* to recreate the state of the star by looking at the correlations among the photons that come out. But it's not impossible. In the second case, the conventional picture of Hawking radiation implies that there is no correlation among the photons, so the information is genuinely completely lost. To answer the questions you must have a clear definition of what information means and what a pure and mixed quantum states are. Yes, but this is standard quantum mechanics. You can make up your own definitions, but then you'll no longer be talking about the same problem. To start with the second, my interpretation of a pure quantum state is that an object as such is completely everywhere physical and chemical identical. They have no structure. The four important parmeters a Radius, Volume, Mass and density. In a pure quantum state object the density is everywhere the same. This is not what the term means. My interpretation of a mixed state is that it has a structure. For example in the Sun and in planets when you "travel" towards the center the density changes. This is also not what the term means. There's a nice explanation in the Wikipedia page under "Density matrix." If you want to talk about the black hole information paradox, you need to use the correct definitions. When the density and chemical composition inside a BH is everywhere the same than the information content is zero compared to the encyclopedia britanica. The text of a book contains knowledge and information. Along that line when you burn a book it is information loss. That's not what "information" means in this context. In the black hole information loss problem, the term "information" has a very specific, technical meaning  it's described by the von Neumann entropy of the density matrix. [...] When the black hole has completely evaporated, The issue is here how do we know that BH physical can evaporate and change into a gaseous (visible?) state. "Evaporation" here has nothing to do with "gaseous"  it just means that the mass of black hole is converted completely to Hawking radiation. How do we know this happens? By doing a computation in quantum field theory to predict the evolution of a black hole. Now, the answer to the paradox may be that we're doing the computation wrong, but that's not a real answer unless you can say exactly *where* the computation is going bad. The problem only appears quantum mechanically, when you allow black holes to evaporate thermally via Hawking radiation. The problem is much more a physical, chemical problem. No, it's not. You are free to invent a different problem, but that's not the one that's called the black hole information paradox. Steve Carlip 
#8




Paradox unexplained
Le 01/04/2016 16:47, Jos Bergervoet a écrit :
For the black hole information paradox I would expect two seemingly conflicting results (as is necessary for a paradox by definition,) e.g. like: 1) We know that information is lost because [...] 2) But also that it is not lost because [...] Unfortunately I cannot find it clearly explained in that way. To be honest, I cannot even find the first statement clearly explained. What I mean is: by using KruskalSzekeres coordinates we can follow any molecule, or larger object, that enters the black hole, and there is no clear indication that it ever loses information at all! There might be tidal forces tearing it apart, but that need not in general destroy information and also that need not happen at the event horizon (in fact the Schwarzschild radius has no special local properties at all, as the KS coordinates prove). Finally, singularities may be present somewhere inside, but we don't know the physics there, so we cannot claim anything about what happens to information at those sites. Actually, for statement 2) I also never found a really satisfying explanation, but let's leave that out, since without *two conflicting statements* there is no paradox anyway. So why do people feel there is a paradox?! A very good introductory article is in the magazine Aeon https://aeon.co/essays/istheblack...antumcomputer 
#9




Paradox unexplained
Op vrijdag 8 april 2016 23:21:25 UTC+2 schreef jacobnavia:
Le 01/04/2016 16:47, Jos Bergervoet a écrit : So why do people feel there is a paradox?! A very good introductory article is in the magazine Aeon https://aeon.co/essays/istheblack...treaquantum= computer Sorry but I have troubles with this article. It starts with the text: "But according to the laws of quantum mechanics, all of the information about your body's build and function will prevail. The relations between the atoms, the uncountable particulars that made you you, will remain forever preserved, albeit in unrecognisably scrambled form  lost in practice, but immortal in principle." This seams like a simple text but it is very difficult to prove that it is true. What means "body's build and function"? If this is not clear then the whole text is not clear and indirect its "deeper" meaning. Next we read: "according to our current physical understanding, information cannot survive an encounter with a black hole." The problem is what has the concept of "information" to do with the physical evolution of a BH? Next we read: "the information paradox makes it aptly clear that physicists still do not understand the fundamental laws of nature." No it does not. The problem is we do not know the details of the physical processes involved in the lifecycle process of BH's. And IMO this has nothing to do with the information paradox which is also not clear. When you study QM, for example https://en.wikipedia.org/wiki/Densit...d_mixed_states you can see what this means related to (polarized) light. This seems rather simple. The problem is how can you use that in the context of the above stated problem: "body's build and function". How can you use that in relation to the lifecycle of a star who becomes a red giant or supernova. I think that is tricky. Nicolaas Vroom 
#10




Paradox unexplained
In article ,
Nicolaas Vroom writes: "But according to the laws of quantum mechanics, all of the information about your body's build and function will prevail. The relations between the atoms, the uncountable particulars that made you you, will remain forever preserved, albeit in unrecognisably scrambled form  lost in practice, but immortal in principle." This seams like a simple text but it is very difficult to prove that it is true. One doesn't prove it directly, but proves the underlying assumptions, from which it follows. What means "body's build and function"? Essentially all information about the body. "according to our current physical understanding, information cannot survive an encounter with a black hole." The problem is what has the concept of "information" to do with the physical evolution of a BH? A lot. Again, and this has already been pointed out here, according to GR a black hole is COMPLETELY characterized by mass, angular momentum, and charge, so there is no record left of what went into it. "the information paradox makes it aptly clear that physicists still do not understand the fundamental laws of nature." No it does not. Yes it does. The problem is we do not know the details of the physical processes involved in the lifecycle process of BH's. Unless you have some alternative theory which shows that information is NOT lost, then the processes are irrelevant. And IMO this has nothing to do with the information paradox which is also not clear. It's not a matter of opinion; it's a matter of using the terms like everyone else uses them. 

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